High frequency transmitter system



Feb. 18, 1941'.

R. 'sEnniLlauzHl HIGH FREQUENCY TRANSMITTER SYSTEM Filed March 18, 1939Patented Feb. 18, 1941 UNITED STATES HIGH FREQUENCY TRANSMITTER SYSTEMRudolf Seidelbach, Berlin, Germany, assigner to C. LorenzAktiengesellschaft, Berlin-Tempelhof,

Germany, a company Application March 1s, 1939, serial No. 262,609 InGermany March 19, 1938 2 Claims.

This invention relates to high frequency transmitter systems, and moreparticularly to new and useful means for reducing the power consumptionof such systems.

It is known in connection with high frequency systems to effectivelyradiate high frequency carrier waves only in presence of modulationvoltages which are to be transmitted. It has been common practiceheretofore to provide relays for correspondingly controlling the carrierfrequency dependent upon the presence or absence of modulationoscillations in such manner that a continuous current derived from themodulation currents is applied to these relays which in response to thepresence of modulation oscillations immediately render the carrierfrequency generator eifective to produce a carrier frequency. Thismethod of carrier frequency control is considerably disadvantageoussince it is impossible to secure reliable transmission of the initialpart of the modulation oscillations since the carrier frequencytransmission lags behind the modulation due to an inevitable delaycaused bythe mechanically operated switching means, from which followsthat arrangements of this type are unsuitable in connection with two-waycommunication systems, or in cases that the effective transmission isfrequently interrupted by silent periods or pauses.

The present invention has for an object to avoid the aforementioneddisadvantages by so controlling the carrier frequency in dependency uponmodulation oscillations that the effective carrier frequency emission isstarted with possibly short delay of time, while the carrier frequencybecomes suppressed with a considerable delay of time after themodulation oscillations have decayed. The immediate' effectiveness ofthe carrier frequency may by way of an example be achieved by a directvoltage control, while the delayed ineffectiveness may be attained bythe agency of a relay arrangement, the individual members of which arerendered slow to operate. An arrangement designed in accordance withthis teaching provides the important feature that the carrier frequencyimmediately involves its desired full amplitude at the very commencementof modulating message or communication current oscillations. Moreover,only transmission interruptions exceeding a predetermined period of timewill cause the suppression of the carrier frequency, while thisfrequency remains effective during short pauses or silent periods of thetransmitter. It is thus possible to reduce the power consumption of suchtransmitter systems in a relevant manner without introducing anypossibilities for message transmission distortions or other troubles ofany kind.

The useful improvement according to my invention hereinafter moreprecisely described is particularly well applicable to speech modulatedhigh frequency broadcasting and communication transmitters, incontradiction to the heretofore known systems'which operate on themethod of controlling the effectiveness and ineffectiveness of thecarrier amplitude with the same time constant according to which thecar-rier becomes entirely suppressed even in response to the shortestinterruption of the modulating speech current supply. It is obvious thatthe transient and frequently occurring suppression of the carrier wavein a transmitter system will inevitably set up distortionsv and otherharmful disturbances in amplitude controlled receiving equipments inwhichit is desirable to pick up messages being radiated from suchsystem,

In cases that specic operating conditions would so require, means may beprovided in order` to subject the amplitude of the carrier frequency toan additional control in response to the amplitude of the modulationoscillations during the intervals of radiation, that is to say, when thecarrier frequency is actually eiective.

My invention may be realized in such manner that a portion of themodulation currents is applied to a rectier device, thereby causing theresultant continuous current from this rectifier to change the grid biasof a transmitter tube to a less negative value. This rectifier isfollowed by smoothing elements such as a iilter, the time constant ofwhich is short enough to ensure that the carrier amplitude is set upsimultaneously with the occurrence of modulation amplitudes. Apparentlythe step of carrier amplitude suppression would be effected inaccordance with the same time constant with which the amplitude of thiscarrier was rendered eifective, but it is an object of this invention toprovide means in order to considerably delay the step of carrierfrequency suppression.

The invention will be more readily understood from the followingdescription taken in conjunction with theaccompanying drawing, thesingle figure of which diagrammatically shows a transmitter system towhich my invention is applied.

In the embodiment shown in this drawing a transmitter I is assumed tohave the six stages I, II, III, IV, V and VI. It will be assumed thatthe stage I consists of a generator for producing a high frequencycarrier and that the amplitude of this carrier is subjected to a controlin the stage IIl by any suitable means, so that when no signal is beingtransmitted the carrier is suppressed. When signal is being transmittedsome means, for example a relay or grid bias control, renders thecarrier operative for transmission. The high frequency carrier ismodulated with modulation oscillations applied to the stage IV in anysuitable manner (not shown) from a modulation frequency source. Aportion of the such as filter units are provided. The direct currentfrom the output side of the rectifier GL' is applied to a directcurrent' amplifier GV and" the output continuous voltage fromthisamplifier is conveyed to the carrier amplitude control stage II inorder to control the carrier amplitude. The potential output fromamplifier A GV may control the carrier output at II by anyfnknown' meansas outlined above, so that the carrier is transmitted as long as theamplifier GV-is operating to produce an output. 'Ihe time constant ofthis control is very low in order to effect the above mentionedamplitude control in time coincidence with the displacement of theoperating'point along the characteristic curve of the amplifier.Simultaneously also a portion of the 'modulation currents is applied toa further rectifier device GM through an amplifier V. This rectifier mayform part of the grid circuit ofy a tube R having a relay P connected inits anode circuit. In the embodiment of my invention a polarized relayis shown in this position although other types of relays maybe usedwithout departing from the scope thereof. It is readily to be observedfrom the diagram shown that a given potential is applied to thecontinuous current amplifier GV over the contact or armature of relay Pin its lefthand position shown and lthrough the adjustable resistor W,so that the amplitude of the carrier is maintained at a given ,value inthe control stage II.

Any change subjected to either of the modulation voltages applied to thedirect current amplifier GV through the modulation frequency amplifier Mwould immediately cause 'the decay of the carrier amplitude on accountof the resultant Voltage change in the first mentioned amplifier, and4this decay would be performed with a time constant which corresponds tothe time constant of, the smoothing means forming part of the rectifierGL. However, in the arrangement under consideration the aforementionedvoltage change cannot Atake place since a constant voltage is appliedtothe amplifier GV over the armature of the polarized relay P in itsposition shown and through the resistor W to maintain an output currentfrom GV, so that the amplitude of the carrier frequency, e. g. onceadjusted to its full value or to 60 per cent of this Value, will be`maintained at constant magnitude.

The time constant of the polarized relay control circuit may be fixed toapproximately 20 to seconds. The desired timing is attained by theagency of a further relay A likewise included in lthe anode circuit ofthe heretofore mentioned to operate.

tube R in series withone winding of the polarized relay P. This relay Acloses its contact al as soon as the cathode-anode path of tube R isrendered non-conductive in response to a modulation frequency decay.Contact al in its right hand position prepares a function circuit .for afurther relay B through a timed resistor UI of uranium dioxide, forexample, the resistance valuev of which becomes strongly reduced afterthe elapse of several seconds so as to complete the function circuit inwhich the relay B is caused Relay B energized closes its contacts bl andb2. The contact bl bridges the re- Kand to close its contacts.

flation oscillations and the energization of the Vsecond winding ofrelay P. The energization of this second winding moves the armature ofrelay P into its right hand position thereby interrupt- A ing the directcurrent supply to the resistor W of the continuous current amplifier GVwith the result that the carrier amplitude is brought down to zero valueafter a predetermined interval of time.

What is `claimed is:

1. A high frequency transmitter system comprising, a generator forproducing a high frequency carrier, means to control the amplitude' ofsaid carrier, a modulation frequency source means to modulate saidcarrier with modulation oscillations from said source, means `fordivertving a first portion of modulation oscillations from said source,mean to rectify and filter said first portion. an amplifier tube havinga grid and an anode, said grid being controlled by said rectified andfiltered first portion of modulation oscillations, said anode beingconnected with said carrier amplitude control means to immediately bringthe amplitude of said carrier to its desired full value in response tothe presence of modulation oscillations, means for diverting a furtherportion of modulation oscillations from said source, and l'meansresponsive to said further portion to maintain the bias of said gridconstantfor a predetermined period of time subsequent to a modulationoscillation decay for holding the amplitude of said carrier. at itsdesired full value during this period.

2. A high frequency transmitter system as defined in claim 1, in whichsaid means responsive to the further portion of modulation oscillationscomprise an amplifier followed by a rectifier, a discharge tube having agrid and an anode, said grid being controlled in response to modulationoscillations from said rectifier, a polarized relay having two windings,and a slow operating relay chain having a time constant of 20 to 30seconds and comprising a first, a second and a third relay, one windingof said polarized relay and the winding of said rst relay being seriallyconnected with said anode to cause said polarized relay to establish acircuit for holding the grid bias of said amplifier tube and thus theamplitude of ySaid carrier'constant 'during the presence of modulationoscillations and to start the operation of said second and said thirdrelay in response to a decay of modulation oscillations for causing saidlast mentioned relays to energize 'the second winding of said polarizedrelay for

